Thermal Stability of High Voltage Li1-xMn1.5Ni0.5O4Cathode Material Synthesized via a Sol-Gel Method

The thermal stability of a high-voltage spinel cathode (LiMn 1.5 Ni 0.5 O 4 ), synthesized via a sol-gel method, was investigated using Accelerating Rate Calorimetry (ARC) and compared to that of LiMn 2 O 4 . Both cathode materials crystallize in the Fd 3 ¯ m space group with nearly identical surface areas (∼0.65 m 2 g −1 ), but they show different microstructures and morphologies that affect their reactivity. In the presence of 1 M LiPF 6 in ethylene carbonate (EC): diethyl carbonate (DEC) (1:2 v/v) electrolyte, both materials show an exothermic surface reaction that is dependent on the cathode morphology, at relatively low temperatures (below 200°C). The onset temperature of the self-heating reaction for Li 1-x Mn 1.5 Ni 0.5 O 4 sample is found to be as low as 60°C (compared to 140°C for Li 1-x Mn 2 O 4 ), significantly affecting the thermal stability of a whole battery containing LiMn 1.5 Ni 0.5 O 4 as the cathode. The decomposition of the spinel material takes place at 195°C for Li 1-x Mn 1.5 Ni 0.5 O 4 and at 215°C for Li 1-x Mn 2 O 4 , with significantly higher self-heating rates for Li 1-x Mn 1.5 Ni 0.5 O 4 than for LiMn 2 O 4 . Our results show that, above 200°C, Ni 4+ is reduced to the more stable Ni 2+ oxidation state and the oxygen released from the cathode during this reaction fuels the combustion of carbonate solvents.